1. Field
The present invention relates to a balancer device for a parallel twin cylinder internal combustion engine.
2. Description of Related Art
Patent Literature 1 (JP-A No. 2011-43189) discloses a primary balancer device (hereinafter called a balancer device) provided in an internal combustion engine including a plurality of cylinders. The balancer device is configured to reduce a primary vibration generated with the same rotational period as a crankshaft, out of vibrations caused by rotation of the crankshaft.
The balancer device according to Patent Literature 1 is configured in such a manner that a balancer weight (balancer) is provided on balancer shafts, and two balancer shafts are used. Such a balancer device is generally called a biaxial primary balancer.
It is publicly known that in the case of a parallel twin cylinder internal combustion engine, if crank phase angles are set at regular intervals, vibration resulting from inertial force included in a primary vibration, or vibration resulting from couple, can be canceled by the crankshaft itself, thereby facilitating setting of the balancer device (arrangement or the like of the balancer).
However, in order to characterize the output characteristics (torque variation or the like) of the parallel twin cylinder internal combustion engine, the crank phase angles are set at irregular intervals (for example, a 270-degree phase crank), complex vibration with inertial force or couple out of the primary vibration included, thereby increasing restrictions on setting of the balancer device. As a result, the balancer occupies most of a space in a crankcase, and restrictions may be imposed on setting of the parallel twin cylinder internal combustion engine.